Challenge solutions

このページは、 CSS Getting Started チュートリアルにあるチャレンジの解答例です。これ以外の解答も考えられます。以下の章名はチュートリアルページのタイトルと一致します。

CSS をなぜ用いるか

Colors

Challenge

Without looking up a reference, find five more color names that work in your stylesheet.

Solution

CSS supports common color names like orange, yellow, blue, green, or black. It also supports some more exotic color names like chartreuse, fuschia, or burlywood. See CSS Color value for a complete list as well as other ways of specifying colors.

どのように CSS は動作するのか

DOM inspector

Challenge

In DOMi, click on a STRONG node. Use DOMi's right-hand pane to find out where the node's color is set to red, and where its appearance is made bolder than normal text.

Solution

In the menu above the right-hand pane, choose CSS Rules.  You see two items listed, one that references an internal resource and one that references your stylesheet file. The internal resource defines the font-weight property as bolder; your stylesheet defines the color property as red.

接続と継承

Inherited styles

Challenge

Change your stylesheet so that only the red letters are underlined.

Solution

Move the declaration for underlining from the rule for <p> to the one for <strong>. The resulting file looks like this:

p {color: blue; }
strong {color: orange; text-decoration: underline;}

Later sections of this tutorial describe style rules and declarations in greater detail.

セレクター

Second paragraph blue

Challenge

Without changing your HTML file, add a single rule to your CSS file that keeps all the initial letters the same color as they are now, but makes all the other text in the second paragraph blue.

Solution

Add a rule with an ID selector of #second and a declaration color: blue;, as shown below:

#second { color: blue; }

A more specific selector, p#second also works.

Both paragraphs blue

Challenge

Now change the rule you have just added (without changing anything else), to make the first paragraph blue too.

Solution

Change the selector of the new rule to be a tag selector using p:

p { color: blue; }

The rules for the other colors all have more specific selectors, so they override the blue of the paragraph.

読みやすい CSS

Commenting out a rule

Challenge

Comment out part of your stylesheet, without changing anything else, to make the very first letter of your document red.

Solution

One way to do this is to put comment delimiters around the rule for .carrot:

/*
.carrot {
  color: orange;
}
*/

文章のスタイル

Big initial letters

Challenge

Without changing anything else, make all six initial letters twice the size in the browser's default serif font.

Solution

Add the following style declaration to the strong rule:

  font: 200% serif;

If you use separate declarations for font-size and font-family, then the font-style setting on the first paragraph is not overridden.

色

Three-digit color codes

Challenge

In your CSS file, change all the color names to 3-digit color codes without affecting the result.

Solution

The following values are reasonable approximations of the named colors:

strong {
  color: #f00; /* red */
  background-color: #ddf; /* pale blue */
  font: 200% serif;
}

.carrot {
  color: #fa0; /* orange */
}

.spinach {
  color: #080; /* dark green */
}

p {
  color: #00f; /* blue */
}

コンテンツ

画像の追加

チャレンジ

各行の初めに画像を表示するように、スタイルシートに一つルールを追加してください。

解答

次のルールをスタイルシートに追加します:

p:before{
  content: url("yellow-pin.png");
}

リスト

小文字のローマ数字

チャレンジ

スタイルシートに一つルールを追加して、リスト項目に i から v のローマ数字で番号をつけてください。

解答

lower-roman のリストスタイルを使って、リスト項目に一つルールを定義します:

li {
  list-style: lower-roman;
}

大文字

チャレンジ

見出しを括弧内の大文字のアルファベットで識別するように、スタイルシートを変更してください。

解答

body 要素（見出しの親要素）にはカウンターをリセットするルールを、見出しにはカウンターを表示し増加させるルールを追加します:

/* numbered headings */
body {counter-reset: headnum;}
h3:before {
  content: "(" counter(headnum, upper-latin) ") ";
  counter-increment: headnum;
}

ボックス

海の境界線

チャレンジ

スタイルシートに一つルールを追加して、リスト項目全体を囲むような広い枠を作り、海を連想するような色にしてください。

解答

次のルールでこの効果を出せます:

ul {
  border: 10px solid lightblue;
}

レイアウト

デフォルトの画像位置

チャレンジ

サンプル文書 doc2.html を編集し、次のタグを文書の末尾近く、</BODY> のすぐ前に追加します: <IMG id="fixed-pin" src="Yellow-pin.png" alt="Yellow map pin"> 画像がどこに現れるか、推測してみてください。それからブラウザを更新して、正しかったかどうかを確認してください。

解答

画像は2番めのリストの右側に現れます。

画像位置の固定化

チャレンジ

スタイルシートにルールを追加して、文書の右上に画像を置くようにしてください。

解答

次のルールでできます:

#fixed-pin  {
  position:fixed;
  top: 3px;
  right: 3px;
} 

表

Borders on data cells only

Challenge

Change the stylesheet to make the table have a green border around only the data cells.

Solution

The following rule puts borders around only <td> elements that are inside the <tbody> element of the table with id=demo-table:

#demo-table tbody td {
  border:1px solid #7a7;
}

メディア

Separate print style file

Challenge

Move the print-specific style rules to a separate CSS file and import them into your style4.css stylesheet.

Solution

Cut and paste the lines between /* print only */ and /* end print only */ into a file named style4_print.css. In style4.css, add the following line at the beginning of the file:

@import url("style4_print.css") print;

Heading hover color

Challenge

Make the headings turn blue when the mouse pointer is over them.

Solution

The following rule achieves the desired result:

h1:hover {
  color: blue;
}

JavaScript

Move box to the right

Challenge

Change the script so that the square jumps to the right by 20 em when its color changes, and jumps back afterwards.

Solution

Add lines to modify the margin-left property. Be sure to specify it as marginLeft in JavaScript. The following script achieves the desired result:

// JavaScript demonstration
function doDemo (button) {
  var square = document.getElementById("square");
  square.style.backgroundColor = "#fa4";
  square.style.marginLeft = "20em";
  button.setAttribute("disabled", "true");
  setTimeout(clearDemo, 2000, button);
}

function clearDemo (button) {
  var square = document.getElementById("square");
  square.style.backgroundColor = "transparent";
  square.style.marginLeft = "0em";
  button.removeAttribute("disabled");
}